The invention relates to recording and, more particularly, techniques for recording noise reduction.
Magnetic recording media, which include magnetic tape and magnetic disks, are used for storage and retrieval of data. The data are encoded in magnetizations on the recording surface. In particular, the data are encoded in transitions, which represent boundaries between regions of magnetization reversal.
There are two parts to a magnetic recording system. The first part is the magnetic recording medium, which holds the data. A typical magnetic recording medium consists of a thin layer of ferromagnetic material, such as gamma ferric oxide, supported by a non-magnetic substrate. The ferromagnetic material is a material that can be permanently magnetized upon application of an external magnetic field. The ferromagnetic material normally includes magnetic particles mixed with a binder to attach it to the non-magnetic substrate.
The second part to a magnetic recording system is the recording head, which applies the external magnetic field that magnetizes the magnetic recording medium. The recording head is an electromagnet that typically comprises ferromagnetic C-shaped core wrapped with a wire coil. The core includes a very narrow gap that is positioned near the magnetic recording medium.
The recording head is energized when current flows through the coil. Current in the coil induces a magnetic flux in the core and causes a fringing magnetic field, also called the recording field, to be generated across the gap. The recording field, which normally has an arcuate or substantially circular profile, extends from the gap through the magnetic recording medium. The recording field gradient is sharper near the gap and broader further from the gap. When the recording field passes through the magnetic recording medium, a remnant magnetization is created on the ferromagnetic surface. This results in a permanent magnetization of the ferromagnetic surface.
When any data stored magnetically are recovered from a magnetic recording medium, there is a risk that the data are contaminated with noise. Generally speaking, noise represents undesirable, unpredictable and random signals. In creating a magnetic recording system, it is desirable to identify sources of noise and, if possible, to reduce or eliminate them.
In general, the invention allows for noise reduction in the magnetic recording medium. More specifically, the present invention allows for the reduction of what herein will be referred to as xe2x80x9ctone noise,xe2x80x9d relating to recording of transitions. Tone noise is caused by at least two sources: position jitter and transition width broadening. Stray magnetic dipole fields from the roughness of layer interfaces are an additional source of medium noise. Each of these sources contributes to undesirable noise on the magnetic recording medium.
The invention reduces noise by including a highly permeable particulate soft magnetic underlayer proximal to the recording layer. The permeable layer modifies the recording magnetic fields extending from the recording head gap by shunting the field into the permeable underlayer. In effect, the permeable magnetic underlayer shapes the recording field, and thereby shapes the recorded transitions.
The permeable magnetic underlayer causes the formation of an image recording field of opposite polarity to the real recording field. The image field behaves as though the field were generated by an image recording head. When the recording layer is thin, the magnetic field behaves as though one pole of the real recording head is closer to the opposite pole of the image recording head than to the opposite pole of the real recording head. As a result, the recording field from one pole of the recording head is drawn to opposite pole of the image recording head, rather than to the opposite pole of the real recording head.
As a consequence of the image in the permeable magnetic underlayer, the recording field penetrating the recording layer has a substantial perpendicular component, and a greatly reduced horizontal component. Moreover, the shape of the recording field has reduced sensitivity to changes in the distance between the recording head and the surface of the medium.
In this way, the recording field records magnetic transitions that are consistently shaped. These characteristics of the transitions reduce position jitter and transition width broadening, and thereby reduce tone noise. In addition, the permeable magnetic underlayer reduces the noise effects of stray magnetic dipole fields. In these ways, a magnetic recording medium with a permeable magnetic underlayer records data with less noise, and therefore has an improved signal-to-noise ratio.
In one embodiment, the invention presents an apparatus comprising a magnetic recording head having a gap and a magnetic recording medium. The magnetic recording medium has a recording layer and a permeable magnetic underlayer proximal to the recording layer. The thickness of the recording layer is less than or equal to one-half the width of the gap.
In another embodiment, the invention presents a magnetic recording medium comprising a recording layer, a substrate and a permeable magnetic underlayer between the recording layer and the substrate. The permeable magnetic underlayer alters a recording field passing through the recording layer. The permeable magnetic underlayer alters the a recording field, for example, by increasing a perpendicular component of the recording field.
In a further embodiment, the invention presents a magnetic recording medium. The medium comprises a recording layer, a permeable magnetic underlayer adjacent the magnetic recording layer and a substrate. The thickness of the recording layer is selected as a function of the width of a gap on a recording head. The invention further presents a method for making such a medium.
In an additional embodiment, the invention presents a method comprising passing a recording field through a recording layer of a magnetic recording medium and regulating the shape of the recording field with a permeable magnetic underlayer. The method may further include regulating a perpendicular component of the recording field with the permeable magnetic underlayer.
Additional details of various embodiments are set forth in the accompanying drawings and the description below. Other features, objects and advantages will become apparent from the description and drawings, and from the claims.